The invention relates to circuit-breakers.
A circuit-breaker has been proposed in which a fixed contact in first chamber is engageable by a hollow movable contact and in which gas, such as sulphur hexafluoride SF.sub.6, in the first chamber is thermally expanded upon the occurrence of an electric arc formed as the contacts are separated. The resultant flow of gas from the first chamber through the hollow moving contact to a second chamber is a blast of gas which extinguishes the arc.
The same proposal included the provision of a coil through which current flows after the arc has commutated from the fixed contact, the arc being made to rotate by a magnetic field caused by the current flowing in the coil. In that proposal one end of the coil is connected directly to one of the terminals of the circuit-breaker and the fixed contact is directly connected to the same terminal. The other end of the coil is connected to an electrode to which the arc commutates. No current therefore flows through the coil when the contacts are engaged.
In that proposal no magnetic field is available to rotate the arc until the arc has commutated and the proposal describes a coil having a relatively large number of turns which produce a magnetic field of relatively high strength.
The coil in that proposal is not associated with any ferromagnetic material to concentrate the magnetic field.